This prospective twin study is designed to determine the genetic component in otitis media (OM) by using like-sex mono- and dizygotic (MZ and DZ) twins. The twin pairs enrolled as newborns are examined at monthly intervals. At each monthly visit an interval history is obtained and middle ear status and hearing sensitivity (every two months) are assessed. Zygosity testing is performed at age one year and consists of extensive red blood cell marker and enzyme determination which gives a probability of greater than 0.99 for monozygosity in completely concordant pairs. The advantages of this study design are two-fold. First, the use of twins allows for separation of genetic and environmental factors in predisposition to OM. Second, the prospective aspect allows for the accurate assessment of disease state and eliminates dependency on recalled information. In this unique cohort of children with documentation of middle ear status since birth, the heritability of immune status can also be assessed and information gained will enhance our understanding of the pathogenesis, complications and sequelae of the disease. Should a substantial genetic component be defined, this study would make a significant clinical contribution by influencing the primary care physician to identify the siblings and offspring of affected patients as "high risk" cases. Closer surveillance of patients at risk for OM could result in earlier detection, treatment and avoidance of possible developmental problems. The study design will also provide the incidence, prevalence, and natural history of OM in this young population. In addition, blood samples for DNA extraction and B-cell immortalization will be collected from all children. The DNA and Epstein-Barr virus immortalized cell lines will be used to establish a specimen repository for future molecular genetic studies including quantitative trait loci mapping. The present proposal is only requesting funds to complete the follow-up of enrolled twin pairs and perform the data analysis.